Electrolytic plating equipment and electrolytic plating method

ABSTRACT

An electrolytic plating equipment includes: a plating tank for holding plating solution; and a separate tank apart from the plating tank, for holding the plating solution circulating between the plating tank and the separate tank. The separate tank contains a first space and a second space located downstream from the first space. The plating solution in the first space in an amount exceeding a specific height flows from the first space into the second space, and the plating solution falls through air in the second space.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrolytic plating equipment andan electrolytic plating method.

2. Background Art

Electrolytic plating is used for forming wiring patterns on printedboards for example. In copper sulfate electrolytic plating for example,various additives including suppressors and promoters (calledbrighteners, carriers, levelers and the like) are added to the platingsolution to obtain coating performance in terms of improved gloss,physical coating properties, throwing power, blind via hole filling andthe like.

Of these additives, suppressors work effectively on the board surface,while promoters work effectively in the through holes and blind viaholes to promote throwing of the through holes and filling of the blindvia holes. If there is too much promoter in the plating solution,however, the ability of the suppressor to suppress growth of activenuclei will be reduced, resulting in a less dense coating with inferiorphysical properties. The effect of controlling precipitation on theboard surface will also be reduced, causing problems with throwing ofthe through holes, filling of the blind via holes and the like. If thereis too little promoter in the plating solution, on the other hand, itwill be less able to promote formation of active nuclei, resulting in aless dense coating with inferior physical properties. The promotingeffects within the through holes and blind via holes may also beinsufficient, causing problems with throwing of the through holes,filling of the blind via holes and the like. Consequently, a suitablebalance of the various additives in the plating solution is important.

The dissolved oxygen concentration of the plating solution is known asone factor the affects the coating performance of electroplate. Thereasons for this are explained by means of an example usingbis(3-sulfopropyl)disulfide (SPS), a common brightener in copper sulfateelectrolytic plating. That is, a sequence of oxidation-reductionreactions such as the following occurs during plate processing. SPS isreduced on the surface of the cathode, becoming 3-mercapto-1-propanesulfonic acid (MPS).

SPS acts as a promoter by reducing copper ions when two MPS dimerizes toreform one SPS near the cathode. MPS not participating in this reactionis oxidized by dissolved oxygen to reform SPS. If the dissolved oxygenis insufficient, however, MPS binds to Cu⁺, and accumulates as Cu⁺-MPS.When Cu⁺-MPS accumulates the brightener concentration becomes too high,and the desired coating performance cannot be obtained. If the oxygenconcentration is too high, more MPS is oxidized by the oxygen, and lessMPS is available for reducing the copper ions, detracting from thepromoting effects so that the desired coating performance are notsufficiently obtained.

Thus, the dissolved oxygen concentration in the plating solution needsto be adjusted to the appropriate range, but when soluble anodes areused, dissolved oxygen is expended in dissolving metal copper and thelike, reducing the dissolved oxygen concentration of the platingsolution, while when insoluble anodes are used, the dissolved oxygenconcentration of the plating solution increases because the anodesgenerate oxygen. A variety of techniques have therefore been proposedfor adjusting the dissolved oxygen concentration of the plating solutionto a specific range.

For example, Japanese Patent Application Laid-open No. 2004-143478discloses an electrolytic plating equipment using soluble anodes as theanodes. This equipment is provided with a plating tank for holding theplating solution and a separate tank apart from the plating tank, andhas a structure in which the plating solution circulates between theplating tank and the separate tank. It is claimed that with thisequipment, the problem of reduced coating quality can be solved byblowing air into the plating solution in the separate tank via an airblowing nozzle to thereby maintain the dissolved oxygen concentration ofthe plating solution at 5 ppm or more.

Japanese Patent Application Laid-open No. 2007-169700 discloses anelectrolytic plating method using insoluble anodes as the anodes. It isclaimed that with this method, non-penetrating holes in a material to beplated can be filled stably for a long period if the plating solution isagitated in the plating tank with air or inactive gas to maintain adissolved oxygen concentration of 30 mg/liter or less.

The required level of plating quality has increased in recent years,however, as the wiring, through holes, blind via holes and the like inprinted boards have become smaller. When there is floating foreignmatter in the plating solution, for example, nodules (a portion in theform of a swelling) may form in part of the coating around this foreignmatter, so electrolytic plating equipments are equipped with filter forseparating foreign matter from the plating solution. This filter iscapable of filtering out various kinds of foreign matter from theplating solution.

However, if many copper or other metal particles adhere to the filterfor example, the dissolved oxygen in the plating solution may beexpended by the metal particles, or additives (such as sulfur additivesand the like) in the plating solution may be affected. Consequently, thefilter must be replaced frequently to prevent a loss of quality of theplating.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an electrolyticplating equipment and electrolytic plating method whereby the dissolvedoxygen concentration of a plating solution can be adjusted and costsassociated with filter replacement reduced.

The electrolytic plating equipment of the present invention includes: aplating tank for holding the plating solution; and a separate tank apartfrom the plating tank, for holding the plating solution circulatingbetween the plating tank and the separate tank. This separate tank hastherein a first space and a second space located downstream from thefirst space, and has a structure in which the plating solution in anamount exceeding a specific height in the first space flows from thefirst space into the second space, and the plating solution fallsthrough air in the second space.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the electrolytic plating equipment of the first embodimentof the present invention;

FIGS. 2A to 2F show modified examples of the structure of the upper edgein the separate tank of the electrolytic plating equipment;

FIGS. 3A to 3E show modified examples of the shape and arrangement ofthe source pipe;

FIG. 4 shows the separate tank of the electrolytic plating equipment ofthe second embodiment of the present invention;

FIG. 5 shows the separate tank of the electrolytic plating equipment ofthe third embodiment of the present invention;

FIG. 6 shows the electrolytic plating equipment of the fourth embodimentof the present invention;

FIG. 7 shows the electrolytic plating equipment of the fifth embodimentof the present invention;

FIGS. 8A and 8B show the plating tank of the electrolytic platingequipment of the sixth embodiment of the present invention;

FIGS. 9A and 9B show the plating tank of the electrolytic platingequipment of the seventh embodiment of the present invention;

FIG. 10 shows the electrolytic plating equipment of the eighthembodiment of the present invention;

FIG. 11A shows the first partition of the separate tank of theelectrolytic plating equipment of the ninth embodiment of the presentinvention, and FIG. 11B shows the XIB-XIB cross-section in FIG. 11A;

FIG. 12 shows the electrolytic plating equipment used in Example 1;

FIG. 13A shows the electrolytic plating equipment used in Example 2, andFIG. 13B shows the XIIIB-XIIIB cross-section in FIG. 13A;

FIG. 14 shows the electrolytic plating equipment used in Example 3;

FIGS. 15A and 15B are a cross-section for explaining the method ofmeasuring pit of the blind via holes in Examples 1 and 3;

FIG. 16 is a plane view showing the shape of a test sample used tomeasure elongation and tensile strength in Examples 1 to 3; and

FIG. 17 is a cross-section for explaining the method of evaluatingthrowing power of the through holes in Example 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Embodiments of the present invention are explained in detail below withreference to the drawings. In the following embodiments, the inventionis explained with reference to examples in which an object is platedwith copper.

First Embodiment

As shown in FIG. 1, electrolytic plating equipment 11 of the firstembodiment of the present invention is provided with plating tank 13,separate tank 15 apart from plating tank 13, source pipe 29 that sendsplating solution from plating tank 13 to separate tank 15, and returnpipe 41 that returns plating solution from separate tank 15 to platingtank 13.

Plating tank 13 has roughly rectangular, open-topped tank body 47 andoverflow tank 49, which is integrated with tank body 47. Anodes 55 arearranged inside tank body 47. Tank body 47 is configured to allowinsertion of cathode 57, which is the object to be plated.

Anodes 55 are arranged on both sides of cathode 57. Soluble anodes orinsoluble anodes are used for anodes 55. In the case of soluble anodes,copper plates can be used for example. Spherical copper (copper balls)contained in a titanium or other mesh container can also be used for thesoluble anodes. These copper plates or copper balls may be formed fromphosphate-containing copper for example. In the case of insolubleanodes, Ti—Pt coated with indium oxide can be used for example.

Each anode 55 is contained in an anode back 59, which allows the passageof plating solution but not of anode slime. Anode backs 59 are formedfrom a material such as polypropylene or polyethylene for example.

Nozzles 61 are arranged vertically between cathode 57 and anodes 55,facing cathode 57. Each nozzle 61 is provided with multiple spraynozzles (not shown) for spraying plating solution supplied from separatetank 15 via source pipe 41 in the direction of cathode 57. Platingsolution around cathode 57 can be agitated by jets from such nozzles 61.In addition to such agitation by jets, plating solution around cathode57 can also be agitated mechanically with a mechanical agitator such asa squeegee or paddle (not shown). Agitation by jets can also be combinedwith mechanical agitation.

Voltage from a power source (not shown) is applied between anodes 55 andcathode 57. Cathode 57 (the object to be plated) can be electroplated inthis way.

Overflow tank 49 is attached integrally to the side of tank body 47.Plating solution in tank body 47 spills over upper edge 53 of side wall51 of tank body 47 into this overflow tank 49. This overflow tank 49 canalso be provided with a liquid level sensor (not shown) for detectingthe liquid level inside the tank. The liquid level in overflow tank 49can be adjusted by controlling the operation or shutoff of pump 63 basedon the detection results from this liquid level sensor.

Separate tank 15 has roughly rectangular, open-topped separate tank body20 and first partition 21, which divides this separate tank body 20 intotwo spaces. First partition 21 is a roughly rectangular partitionextending upwards from the bottom surface of separate tank body 20. Thisfirst partition 21 divides the inside of separate tank 15 into firstspace 17 and second space 19 located downstream from first space 17. Asshown in FIGS. 1 and 2A, first partition 21 has partition body 25extending from the bottom towards the top of separate tank 15, and lip(extending portion) 27 extending from the top edge of partition body 25towards second space 19.

Upper edge 23 of first partition 21 is set at a specific height belowthe upper edge of separate tank body 20. That is, separate tank 15 has astructure whereby that part of the plating solution that exceeds thisspecific height in first space 17 overflows upper edge 23 and flows fromfirst space 17 into second space 19. In separate tank 15, first space 17and second space 19 only communicate in the space above upper edge 23 offirst partition 21. In the structure of separate tank 15, first space 17and second space 19 are separated so that plating solution does not movebetween first space 17 and second space 19 below upper edge 23.

The plating solution flowing into second space 19 falls through air insecond space 19. The liquid surface of the plating solution in secondspace 19 is adjusted to a position lower than the specific height ofupper edge 23 of first partition 21 so as to cause the plating solutionto fall through air in this way in second space 19.

The liquid surface of the plating solution in second space 19 can beadjusted by controlling the operation or shutoff of pump 64 provided onreturn pipe 41 for example. Second space 19 can also be provided with aliquid level sensor (not shown) for detecting the liquid level insidethis space. The liquid level in second space 19 can be adjusted bycontrolling the operation or shutoff of pump 64 based on the detectionresults from this liquid level sensor.

Lip 27 extends horizontally from the upper edge of partition body 25toward second space 19, and its end is separated from the side surfaceof partition body 25 facing second space 19. With this lip 27, platingsolution flowing from first space 17 into second space 19 is conductedalong lip 27 to the end of the lip 27, where it separates from lip 27and is released into air. Because the outer end of lip 27 is separatedfrom the side surface of partition body 25, the plating solution can berestrained from flowing down the side surface of partition body 25.

In this embodiment, first partition 21 is explained by means of anexample having a lip 27 such as that shown in FIG. 2A, but lips 27 suchas the modified examples shown in FIGS. 2B to 2D are also possible, asare embodiments without lips such as the modified examples shown inFIGS. 2E and 2F.

In the modified example of FIG. 2B, lip 27 extends upwards at an anglefrom the top of partition body 25 towards second space 19. As in theembodiment of FIG. 2A, in this modified example the end of lip 27 isseparated from the side surface of partition body 25. As a result, theplating solution can be restrained from flowing down the side surface ofpartition body 25, but in comparison to FIG. 2A, the plating solution ismore likely to flow along the surface (lower surface) of lip 27 facingsecond space 19.

In the modified example of FIG. 2C, lip 27 extends downward at an anglefrom the top of partition body 25 towards second space 19. As in theembodiment of FIG. 2A, in this modified example the end of lip 27 isseparated from the side surface of partition body 25, and the platingsolution can be restrained from flowing down the side surface ofpartition body 25. Moreover, because lip 27 extends downwards at anangle, the plating solution is almost completely prevented fromcontacting the lower (inner) surface of lip 27. In this respect themodified example of FIG. 2C is superior to the embodiment of FIG. 2A.

In the modified example of FIG. 2D, lip 27 has horizontal part (lateralpart) 27 a extending horizontally towards second space 19 from the topof partition body 25, and vertical part (lower part) 27 b extendingdownwards from the lateral end of horizontal part 27 a. The lower end ofthis vertical part 27 b is separated from the side surface of partitionbody 25. As in FIG. 2A, in this modified example plating solution can berestrained from flowing down the side surface of partition body 25because the end of lip 27 is separated from the side surface ofpartition body 25. Moreover, in this embodiment plating solution flowinginto second space 19 from first space 17 is first conducted alonghorizontal part 27 a to the end of this part, and then flows downwardalong vertical part 27 b. There is a large distance between this edgeand the side surface of partition body 25. Consequently, platingsolution is prevented almost completely from contacting the innersurface of lip 27. In this respect, the modified example of FIG. 2D issuperior to the embodiment of FIG. 2A.

In the modified examples of FIGS. 2E and 2F, first partition 21 has nolip. In the modified example of FIG. 2E, first partition 21 is disposedvertically. In the modified example of FIG. 2F, first partition 21 isarranged at an angle to the perpendicular direction. The first partition21 of this modified example is slanted so that the lower part isdownstream from the upper part.

The upstream ends of source pipe 29 are connected to the bottom ofoverflow tank 49 and to side wall 51 of tank body 47, communicating withoverflow tank 49 and tank body 47. The downstream end of source pipe 29is provided with supply port 29 a, which supplies plating solution toseparate tank 15.

As shown in FIGS. 1 and 3A, supply port 29 a is located above the liquidsurface of the plating solution in first space 17, and does not contactthe plating solution. Consequently, when plating solution dischargedfrom supply port 29 a flows downward from supply port 29 a to contactplating solution held in first space 17, it administers some degree ofshock to this plating solution. This causes some fluid movement of theplating solution in first space 17.

In the modified examples of FIGS. 3B to 3E, supply port 29 a of sourcepipe 29 is located below the aforementioned specific height. That is,supply port 29 a may also be located below the liquid surface of theplating solution in first space 17, so as to be immersed in the platingsolution. In these modified examples, the plating solution dischargedfrom supply port 29 a is supplied directly within the plating solutionheld in first space 17. The shock to the plating solution in first space17 is thus less than in the embodiment of FIG. 3A, in which the platingsolution from supply port 29 a is first discharged into air beforefalling onto the liquid surface of the plating solution held in firstspace 17.

In the modified example of FIG. 3C, the downstream end of source pipe 29is bent so that the plating solution from supply port 29 a is directedtowards inner surface 20 a of separate tank body 20. In this modifiedexample, fluid movement of the plating solution held in first space 17,and particularly plating solution located towards the bottom of thetank, is suppressed more than in the embodiment of FIG. 3B, in which theplating solution is discharged downwards.

In the modified example of FIG. 3D, the downstream end of source pipe 29is branched (into 6 in this modified example), having multiple supplyports 29 a for discharging plating solution. The discharge speed of theplating solution discharged from each supply port 29 a is thus less thanin the modified example of FIG. 3B. Consequently, it is possible tosuppress fluid movement of plating solution held in first space 17, andparticularly plating solution located towards the bottom of the tank.

In the modified example of FIG. 3E, source pipe 29 has a structure inwhich the inner diameter of the downstream end of the pipe is wider thanat other sites. The discharge speed of the plating solution dischargedfrom supply port 29 a is thus less than in the modified example of FIG.3B. Consequently, it is possible to suppress movement of platingsolution held in first space 17, and particularly plating solutionlocated towards the bottom of the tank.

As shown in FIG. 1, the upstream end of return pipe 41 is connected tothe side of separate tank body 20, communicating with second space 19.The downstream end of return pipe 41 is branched into multiple ends (3in this embodiment). Two of these multiple ends, 41 a and 41 b, areconnected to the aforementioned pair of nozzles 61, communicating withnozzles 61. The remaining end 41 c of a plurality of pipe ends isconnected to the bottom of tank body 47, communicating with the insideof tank body 47. This end 41 c is located near the side of tank body 47opposite overflow tank 49.

Filter 65 is attached to return pipe 41 upstream from the branches. Pump64 is provided on return pipe 41 upstream from this filter 65. Operatingthis pump 64 and the aforementioned pump 63 causes plating solution tocirculate between plating tank 13 and separate tank 15. Filter 65 canfilter the plating solution to separate out various kinds of foreignmatter from the liquid.

The bath volume ratio of the plating tank 13 and separate tank 15(volume of plating tank 13:volume of separate tank 15) is preferablybetween 0.1:1 and 30:1 or more preferably between 0.3:1 and 10:1. If thevolume of plating tank 13 is less than 0.1 times the volume of separatetank 15, separate tank 15 will be so large as to be impractical. If thevolume of plating tank 13 is more than 30 times the volume of separatetank 15, on the other hand, the ability to adjust the dissolved oxygenin separate tank 15 may be inadequate.

The circulating volume (turns) is calculated as circulation speed(liters/minute)×60 (minutes/hour)/total capacity (liters), and ispreferably 5 to 100 turns or more preferably 10 to 80 turns relative tototal bath volume (total amount of plating solution circulating in theelectrolytic plating equipment). A circulating volume of less than 10turns may be insufficient for adjusting the dissolved oxygen in separatetank 15. On the other hand, a circulating volume of more than 100 turnsis impractical because it necessitates a large circulation pump orseveral circulation pumps.

A copper sulfate plating solution for example is used as the platingsolution. A copper sulfate plating solution comprises a specific amountof sulfuric acid added to copper sulfate as the copper source. Variousadditives can be added as necessary to this copper sulfate platingsolution. These additives may be organic additives such as suppressorsand promoters, called brighteners, levelers and carriers. Examples ofthese organic additives include nitrogen-containing organic compounds,sulfur-containing organic compounds, oxygen-containing organic compoundsand the like. Specific examples of sulfur-containing compounds includesulfur compounds selected from the following formulae (1) to (4) below.

(wherein R₁, R₂ and R₃ are each C₁₋₅ alkyl groups, M is a hydrogen atomor alkali metal, a is an integer from 1 to 8 and b, c and d are eacheither 0 or 1.)

Well-known nitrogen-containing organic compounds can also be used, suchas tertiary amine compounds, quaternary ammonium compounds and the likefor example. Known oxygen-containing compounds can be used, such aspolyethylene glycol and other polyether compounds for example.

When the components of the copper sulfate plating solution have becomedecreased by continuous electrolytic copper plating, they can bereplenished as necessary by adding a replenishing solution. Continuouselectrolytic copper plating is thus possible. Copper ions can also bereplenished from the soluble anodes when soluble anodes are used. Wheninsoluble anodes are used, a tank capable of supplying copper ions canbe provided separately from plating tank 13, and copper ions in theplating tank can be replenished from this tank.

Next, the operations of electrolytic plating equipment 11 of thisembodiment are explained. During the initial bath makeup, specificquantities of plating solution are deposited in tank body 47 andoverflow tank 49 of plating tank 13, and in first space 17 and secondspace 19 of separate tank 15.

Next, pump 63 and pump 64 are operated to circulate the plating solutionbetween plating tank 13 and separate tank 15. The liquid levels inoverflow tank 49 and second space 19 are adjusted by controlling theoperation or shutoff of pump 63 and pump 64. Under these conditions,cathode 57 as the object to be plated is immersed in the plating bath intank body 47, and current is applied between anodes 55 and cathode 57.The object to be plated is copper electroplated in this way. Whenelectrolytic plating is complete, the object to be plated is replacedwith another object, and successive electrolytic copper plating isperformed.

Next, the flow of plating solution is explained. When pump 64 operates,plating solution is supplied to the inside of tank body 47 via returnpipe 41. When plating solution is supplied to this tank body 47, platingsolution in the same quantity as the liquid supplied flows over top edge53 of side wall 51 of tank body 47, and into overflow tank 49.

When pump 63 operates, the plating solution in overflow tank 49 and tankbody 47 is supplied to first space 17 of separate tank 15 via sourcepipe 29. Foreign matter such as for example slough from cathode 57 orcopper particles resulting from slime generated by the soluble anodesare floating in the plating solution. Copper particles that are denserthan the plating solution drop down in first space 17 of separate tank15 to settle at the bottom of first space 17.

When plating solution is supplied to first space 17 via source pipe 29,meanwhile, plating solution in the same amount as the supplied liquidflows over upper edge 23 of first partition 21 and into second space 19.Plating solution entering second space 19 falls through air in secondspace 19 to arrive at the surface of the plating solution held in secondspace 19. Exposing plating solution to air in this way as it fallsserves to adjust the dissolved oxygen concentration of the platingsolution. Specifically, when soluble anodes are used for anodes 55, adrop in the dissolved oxygen concentration of the plating solution canbe prevented by incorporating oxygen from air into the plating solutionduring plating. If insoluble anodes are used for the anodes, on theother hand, a rise in the dissolved oxygen concentration of the platingsolution can be prevented by discharging oxygen as necessary into airfrom the plating solution during plating.

The dissolved oxygen concentration is adjusted by changing the timeduring which the plating solution falls through air, the surface area ofcontact with air as it falls through air and the like. The time duringwhich the plating solution falls through air and the surface area ofcontact of the plating solution with air as it falls through the air canbe adjusted by changing the distance between the top edge 23 of firstpartition 21 and the surface of the plating solution in second space 19for example, or the width of upper edge 23 overflowed by the platingsolution.

The dissolved oxygen concentration of the plating solution in tank body47 of plating tank 13 can preferably be 4 to 20 mg/liter. If thedissolved oxygen concentration is less than 4 mg/liter or more than 20mg/liter, the quality of the plate may be adversely affected.Specifically, physical coating properties such as the elongation andtensile strength of the plating may decline, or the throwing power (TP)of the through holes in the printed board may be reduced, or filling ofthe blind via holes may be reduced (increased pit).

Since in this embodiment the plating solution in first space 17overflows into second space 19 as described above, air is incorporatedinto the plating solution as it falls due to this overflow. Thedissolved oxygen concentration of the plating solution can thus be madeto approach the saturated dissolved oxygen concentration. Air consistsprimarily of oxygen (about 20%) and nitrogen (about 80%). As abenchmark, the saturated dissolved oxygen concentration of water at 25°C. is about 8.1 mg/liter. When the dissolved oxygen concentration of theplating solution is below the aforementioned desirable range (4 to 20mg/liter), oxygen from the air dissolves into the plating solution as itoverflows and falls through the air, bringing the dissolved oxygenconcentration of the plating solution closer to the saturated dissolvedoxygen concentration. The dissolved oxygen concentration of the platingsolution can thus be easily adjusted to the desirable range. When thedissolved oxygen concentration of the plating solution is above theaforementioned desirable range, on the other hand, part of the oxygenthat dissolved into the plating solution as it overflowed and fellthrough the air is released appropriately into air due to the effect ofthe nitrogen in the air, bringing the dissolved oxygen concentration ofthe plating solution closer to the saturated dissolved oxygenconcentration. The dissolved oxygen concentration of the platingsolution can thus be easily adjusted to the desirable range.

The distance (drop) between upper edge 23 of first partition 21 and thesurface of the plating solution in second space 19 is not particularlylimited, but is preferably at least cm or more preferably at least 15 cmfor purposes of efficiently adjusting the dissolved oxygenconcentration. The drop should also be no more than 100 cm so thatseparate tank 15 does not become too large.

In this embodiment, a configuration in which separate tank has only onepartition and the plating solution overflows only once is given as anexample, but as explained below, overflow can be made to occur more thanonce in separate tank 15 by providing multiple partitions within theseparate tank body. The number of overflows in separate tank 15 ispreferably 2 or more from the standpoint of allowing more efficientadjustment of the dissolved oxygen concentration. The number ofoverflows is preferably 5 or less so that separate tank 15 does notbecome too large.

As explained above, in the first embodiment that part of the platingsolution that exceeds a specific height flows from first space 17 intosecond space 19, while that part at or below the specific height remainsin first space 17. As a result, metal particles in the plating solutionremaining in first space 17 can be made to settle at the bottom of firstspace 17. If the metal particles settle and accumulate in this way atthe bottom of first space 17, it is possible to efficiently remove metalparticles in the plating solution by a collection means such asscheduled collection of the metal particles for example. In this way, itis possible to reduce the frequency of replacing filter 65 inelectrolytic plating equipment 11, and in some cases filter 65 may notbe necessary. The dissolved oxygen concentration of the plating solutioncan also be adjusted by causing that part of the plating solution infirst space 17 that exceeds a fixed height to flow into second space 19and fall through air in second space 19, or in other words by exposingthe plating solution in a flowing state to air. Consequently, with thefirst embodiment it is possible to adjust the dissolved oxygenconcentration of the plating solution and also reduce the costsassociated with filter replacement.

Specifically, when soluble anodes are used as the anodes, it is possibleto prevent a drop in dissolved oxygen concentration of the platingsolution because oxygen from air is incorporated into the platingsolution during plating. When insoluble anodes are used as the anodes,it is possible to prevent a rise in dissolved oxygen concentration ofthe plating solution because a suitable amount of oxygen is releasedinto air from the plating solution during plating.

In the first embodiment, upper edge 23 extends towards second space 19,and its end has lip 27, which is separated from the side of the firstpartition 21. Thus, plating solution flowing from first space 17 intosecond space 19 is conducted along lip 27 to the end of the lip 27,where it separates from lip 27 and is released into air. As a result, inthe first embodiment plating solution is prevented from falling alongthe side of first partition 21. It is thus possible to increase the areaof contact of the plating solution with air as it falls, and thus tomore efficiently adjust the dissolved oxygen concentration of theplating solution.

Second Embodiment

FIG. 4 shows separate tank 15 of electrolytic plating equipment 11 ofthe second embodiment of the present invention. In this secondembodiment, the structure of first space 17 of separate tank 15 isdifferent from that of the first embodiment. Components that are thesame as in the first embodiment are indicated by the same symbols(reference numbers), and detailed explanations are omitted.

As shown in FIG. 4, separate tank 15 has second partition 35 in additionto separate tank body 20 and first partition 21. This second partition35 is roughly rectangular, and extends vertically from the bottom ofseparate tank body 20. Second partition 35 divides the inside of firstspace 17 into two spaces. One space is supply space 33 to which platingsolution is supplied from supply port 29 a of source pipe 29, while theother space, located downstream from supply space 33, is settling space31 for settling metal particles 32 from the plating solution.

Second partition 35 has multiple communicating holes communicatingbetween settling space 31 and supply space 33. These communicating holesare provided below the aforementioned specific height, or in other wordsbelow the height of upper edge 23 of first partition 21. Platingsolution in first space 17 can move from supply space 33 to settlingspace 31 through these multiple communicating holes. A resin plate,metal plate or the like having multiple through holes arranged at fixedintervals across the entire surface can be used as second partition 35for example. The communicating holes are adjusted to a size that allowsat least the passage of metal particles.

In the second embodiment, first space 17 is divided by second partition35 into settling space 31 and supply space 33, and plating solution issupplied from supply port 29 a of source pipe 29 to supply space 33.Therefore, even if plating solution held in supply space 33 undergoesfluid movement when plating solution is supplied, this movement shouldnot be communicated to settling space 31. As a result, metal particles32 can be deposited more efficiently than if there were no secondpartition 35 dividing first space 17.

Moreover, in the second embodiment second partition 35 has multiplecommunicating holes provided below a specific height that communicatebetween settling space 31 and supply space 33. As a result, platingsolution supplied to supply space 33 is dispersed as it moves throughthe multiple communicating holes of second partition 35 into settlingspace 31. Fluid movement of the plating solution held in settling space31 can be suppressed because the plating solution is dispersed as itflows through the multiple communicating holes into settling space 31.

Other configurations, actions and effects are not mentioned here becausethey are the same as in the first embodiment.

Third Embodiment

FIG. 5 shows separate tank 15 of electrolytic plating equipment 11 ofthe third embodiment of the present invention. In this third embodiment,the structure of first space 17 of separate tank 15 is different fromthose of the first and second embodiments. Constituent elements that arethe same as in the first embodiment are indicated by the same symbols,and detailed explanations are omitted.

As shown in FIG. 5, separate tank 15 has second partition 35 in additionto separate tank body 20 and first partition 21. This second partition35 is rectangular, and extends vertically from the bottom of separatetank body 20 as in the second embodiment above. Second partition 35divides the inside of first space 17 into supply space 33 and settlingspace 31. The difference between this and the second embodiment is thatsecond partition 35 of the third embodiment does not have multiplecommunicating holes.

In the third embodiment, upper edge 35 a of second partition 35 ispositioned below the aforementioned specific height so that the heightof upper edge 35 a of second partition 35 is lower than the surface ofthe plating solution held in settling space 31. In this way, platingsolution in first space 17 can move from supply space 33 to settlingspace 31 over upper edge 35 a of second partition 35.

Consequently, because the third embodiment has second partition 35, thefluid movement of plating solution that occurs when plating solution issupplied to supply space 33 from supply port 29 a is unlikely to becommunicated to settling space 31. Moreover, because the platingsolution flows into settling space 31 from supply space 33 over upperedge 35 a of second partition 35, it is possible to prevent metalparticles 32 that have settled at the bottom of the settling space frombeing stirred up again.

Other configurations, actions and effects are not explained because theyare the same as in the first embodiment.

Fourth Embodiment

FIG. 6 shows electrolytic plating equipment 11 of the fourth embodimentof the present invention. This fourth embodiment differs from the firstembodiment in having re-supply pipe 43. Constituent elements that arethe same as in the first embodiment are indicated by the same symbols,and detailed explanations are omitted.

As shown in FIG. 6, in this fourth embodiment electrolytic platingequipment 11 is also provided with re-supply pipe 43 for returningplating solution discharged from separate tank 15 to first space 17. Oneend 43 a of this re-supply pipe 43 is connected to the lower side ofseparate tank body 20, communicating with second space 19. The other end43 b is located above first space 17. Re-supply pipe 43 is provided withpump 66 and filter 68.

Consequently, in the fourth embodiment part of the plating solution insecond space 19 of separate tank 15 can be supplied again to first space17 via re-supply pipe 43 before being returned to plating tank 13.Foreign matter in the plating solution can thus be removed even moreefficiently.

Other configurations, action and effects are not explained but are thesame as in the aforementioned first embodiment.

Fifth Embodiment

FIG. 7 shows electrolytic plating equipment 11 of the fifth embodimentof the present invention. This fifth embodiment differs from the firstembodiment in that underflow divider 45 is provided in second space 19.Constituent elements that are the same as in the first embodiment areindicated with the same symbols, and detailed explanations are omitted.

As shown in FIG. 7, in this fifth embodiment divider 45 is provided insecond space 19 downstream from first space 17. This divider 45 is aplate arranged so that there is a gap between the bottom of separatetank body 20 and the lower edge of divider 45, and second space 19 abovethe gap is divided into two regions of an upstream region and adownstream region. As a result, plating solution flowing from firstspace 17 into second space 19 always passes through this gap as it movesfrom the upstream region to the downstream region within second space19. This results in a more uniform agitation of the liquid in secondspace 19.

Other configurations, actions and effects are not explained in detail,but are the same as in the first embodiment.

Sixth Embodiment

FIGS. 8A and 8B show part of plating tank 13 of electrolytic platingequipment 11 of the sixth embodiment of the present invention. FIG. 8Ashows part of plating tank 13 from the side, and FIG. 8B shows it fromthe top. In the sixth embodiment, the structure of overflow tank 49 ofplating tank 13 is different from that of the first embodiment.Constituent elements that are the same as in the first embodiment areindicated with the same symbols, and detailed explanations are omitted.

As shown in FIGS. 8A and 8B, in this sixth embodiment overflow tank 49of plating tank 13 contains upstream space 71 and downstream space 73,which is located downstream from upstream space 71. Overflow tank 49 iscomposed of two tanks, first tank 75 and second tank 77. Upstream space71 is the space delineated by first tank 75 and side wall 51 of tankbody 47, while downstream space 73 is the space delineated by secondtank 77 and side wall 51 of tank body 47.

Looking at the upper edge 53 of side wall 51 of tank body 47, the upperedge of first tank 75 and the upper edge of second tank 77, the upperedge of second tank 77 is the highest while the upper edge of first tank75 is the lowest. As shown in FIG. 8B, the upper edge of first tank 75is provided with a pair of overflow parts 81. These overflow parts 81are lower than the other parts so that plating solution can overflowfrom first tank 75 into second tank 77. Through hole 79 connecting tosource pipe 29 is provided at the bottom of second tank 77.

Thus, plating solution overflows upper edge 53 of side wall 51 of tankbody 47 into upstream space 71 of first tank 75, then overflows theupper edge of first tank 75 into downstream space 73 of second tank 77,and then flows into source pipe 29 via through hole 79. Thus, the sixthembodiment is configured so that plating solution falls through airtwice. As a result, the dissolved oxygen concentration of the platingsolution can be adjusted not only in separate tank 15 but also inoverflow tank 49 of plating tank 13.

In this sixth embodiment in particular, the dissolved oxygenconcentration can be adjusted efficiently as the plating solution flowsfrom upstream space 71 to downstream space 73 and falls through air ifthe drop from the upper edge of first tank 75 to the liquid surface insecond tank 77 is 10 cm or more.

Upper edge 53 of side wall 51 of tank body 47 preferably has a lipsimilar to that shown in FIG. 2. Similarly, the upper edge of first tank75 preferably has a lip similar to that shown in FIG. 2. When the upperedge has a lip in this way, plating solution flowing from tank body 47into first tank 75 and plating solution flowing from first tank 75 intosecond tank 77 is conducted along the lip to the end of the lip, whereit separates from the lip and is released into the air. As a result, theplating solution can be prevented from flowing along the side surface ofside wall 51 of the tank body 47 or the side surface of first tank 75.In this way, the dissolved oxygen concentration of the plating solutioncan be adjusted more efficiently because the area of contact of thefalling plating solution with air can be increased.

Other configurations, actions and effects are not explained but are thesame as in the first embodiment.

Seventh Embodiment

FIG. 9A and FIG. 9B show one part of plating tank 13 of electrolyticplating equipment 11 of the seventh embodiment. FIG. 9A shows part ofthe plating tank 13 from the side, while FIG. 9B shows it from the top.In the seventh embodiment, the structure of overflow tank 49 of platingtank 13 is different from that of the first embodiment, and thestructure of first tank 75 is different from that of the sixthembodiment. Constituent elements that are the same as in the firstembodiment and sixth embodiment are indicated with the same symbols, anddetailed explanations are omitted.

As shown in FIG. 9A and FIG. 9B, in the seventh embodiment first tank 75has through holes 85 on the bottom surface, and discharge pipes 83connected to these through holes 85. Plating solution in upstream space71 flows through these discharge pipes 83 to fall through air intodownstream space 73. The bottom of first tank 75 is positioned above thebottom of second tank 77. Discharge pipes 83 can be omitted.

Other configurations, actions and effects are not explained but are thesame as in the first embodiment.

Eighth Embodiment

FIG. 10 shows electrolytic plating equipment 11 of the eight embodimentof the present invention. This eighth embodiment differs from the firstembodiment in that there are two overflows in separate tank 15.Constituent elements that are the same as in the first embodiment areindicated with the same symbols, and detailed explanations are omitted.

As shown in FIG. 10, in this eighth embodiment separate tank 15 isprovided with third partition 91. This third partition 91 is rectangularin shape and extends vertically from the bottom of separate tank body20. The inside of separate tank 15 is divided by this third partition 91into second space 19 and third space 93 located downstream from thissecond space 19. In this way, the dissolved oxygen concentration of theplating solution can be adjusted even more efficiently.

In this eighth embodiment, moreover, second space 19 and third space 93,which are downstream from first space 17 for settling metal particles,are provided with underflow dividers 45. As in the fifth embodiment ofFIG. 7, these dividers 45 are plates arranged so that there are gapsbetween the bottom of separate tank body 20 and the lower edges ofdividers 45 in second space 19 and third space 93, and second space 19above the gap is divided into two regions, an upstream region and adownstream region, while third space 93 above the gap is also dividedinto two regions, an upstream region and a downstream region. As aresult, plating solution flowing from first space 17 into second space19 always passes through this gap as it moves from the upstream regionto the downstream region within second space 19, and plating solutionflowing from second space 19 to third space 93 always passes through thegap as it moves from the upstream region to the downstream region withinthird space 93, resulting in a more uniform mixing of the platingsolution in second space 19 and third space 93.

Upper edge 24 of third partition 91 has a structure similar to that ofupper edge 23 of first partition 21. That is, like upper edge 23 offirst partition 21, upper edge 24 of third partition 91 has lip 27, soplating solution flowing from second space 19 into third space 93 isconducted along lip 27 to the end of the lip, where it separates fromlip 27 and is released into air. As a result, plating solution can beprevented from flowing along the side surface of third partition 91. Itis thus possible to increase the contact area of the plating solutionwith air as it falls, and to more efficiently adjust the dissolvedoxygen concentration of the plating solution.

Other configurations, actions and effects are not explained but are thesame as in the first embodiment.

Ninth Embodiment

FIGS. 11A and 11B show first partition 21 of the separate tank of theelectrolytic plating equipment of the ninth embodiment. In this ninthembodiment, plating solution does not overflow the upper edge of firstpartition 21 as in the previous embodiments, but instead flows fromfirst space 17 into second space 19 via through hole 95 provided at theaforementioned specific height in first partition 21.

In the ninth embodiment, the plating solution may fall along the sidesurface of first partition 21 as it flows from first space 17 intosecond space 19, but preferably falls without contacting the sidesurface of first partition 21. For example, as shown in FIG. 11B, firstpartition 21 preferably has lip 95 a protruding laterally from the loweredge of through hole 95 in the side of the partition facing second space19. In this case, plating solution flowing from first space 17 intosecond space 19 is conducted along lip 95 a to the end of the lip 95 a,where it separates from lip 95 a and is released into the air. It isthus possible to prevent the plating solution from flowing along theside surface of first partition 21. In this way, the contact area of theplating solution with air is increased as it falls, and the dissolvedoxygen concentration of the plating solution can be more efficientlyadjusted.

Other configurations, actions and effects are not explained but are thesame as in the first embodiment.

Other Embodiments

The present invention is not limited to the aforementioned embodiments,and various changes and improvements are possible to the extent thatthey do not deviate from the intent of the invention.

For example, in the aforementioned embodiments an object to be platedwas plated with copper in the examples given, but in addition toelectrolytic copper plating the present invention is applicable toelectrolytic nickel plating, electrolytic gold plating and the like forexample.

In the aforementioned embodiments, separate tank 15 is divided by apartition or partitions into 2 or 3 spaces, but separate tank 15 canalso be divided into 4 or more spaces.

Moreover, a re-supply pipe such as that of the fourth embodiment couldalso be provided in the electrolytic plating equipment of anotherembodiment.

The electrolytic plating equipment and electrolytic plating method usingit of the aforementioned embodiments can be used favorably for formingwiring patterns on such plated objects as printed boards, wafers and thelike, but applications thereof are not particularly limited.

The embodiments are summarized below as follows.

The electrolytic plating equipment of the aforementioned embodimentsincludes: a plating tank for holding the plating solution; and aseparate tank apart from the plating tank, for holding the platingsolution circulating between the two tanks. The separate tank hastherein a first space and a second space located downstream from thefirst space, and has a structure in which the plating solution in thefirst space in an amount exceeding a specific height flows from thefirst space into the second space, and the plating solution fallsthrough air in the second space.

With this configuration, since that part of the plating solution thatexceeds a specific height flows from the first space into the secondspace while that part that is at or below the specific height remains inthe first space, metal particles in the plating solution remaining inthe first space can be allowed to settle at the bottom of the firstspace. If metal particles settle and accumulate in this way at thebottom of the first space, it is possible to efficiently remove metalparticles in the plating solution by a collection means such asscheduled collection of the metal particles for example. In this way,filter exchange frequency can be reduced in the electrolytic platingequipment, or in some cases the filter can be eliminated altogether.

The dissolved oxygen concentration of the plating solution can also beadjusted by causing that part of the plating solution in the first spacethat exceeds a specific height to flow into the second space and fallthrough air in the second space, or in other words by exposing theplating solution in a fluid state to air.

In this way, as discussed above, not only can the dissolved oxygenconcentration of the plating solution be adjusted, but costs associatedwith filter replacement can also be reduced.

A specific example of the structure of such a separate tank has apartition extending vertically so as to divide the first space from thesecond space, and has a structure in which the plating solution in thefirst space overflows an upper edge located at the aforementionedspecific height on the partition, and flows into the second space.

In the electrolytic plating equipment according to the above embodiment,the upper edge of the partition has preferably an extending portionextending towards the second space, and the extending portion preferablyhas an end that is separated from the side of the partition.

In this configuration, plating solution flowing from the first spaceinto the second space is conducted along the extending portion to theend of the extending portion, where it separates from the extendingportion and is released into air. That is, when the upper edge of thepartition is not provided with this extending portion, the platingsolution flowing from the first space into the second space is likely tocontact the side surface of the partition and flow along this sidesurface, but in the present configuration the plating solution can beprevented from flowing along the side surface. This serves to increasethe area of contact of the plating solution with air as it falls, sothat the dissolved oxygen concentration of the plating solution can beadjusted more efficiency.

In the electrolytic plating equipment according to the above embodiment,the extending portion preferably has a lateral part extending laterallytowards the second space and a lower part extending downwards from alateral end of the lateral part, and the end of the extending portion isa lower end of the lower part, the lower end is separated from the sidesurface of the partition.

In this configuration, plating solution can be restrained from flowingalong the side surface of the partition because plating solution flowingfrom the first space into the second space is first conducted along thelateral part to the end of this part, thereby increasing its distancefrom the side surface of the partition, and then flows downwards alongthe lower part.

In the electrolytic plating equipment according to the above embodiment,the separate tank may have a partition extending vertically so as todivide the separate tank into the first space and the second space, andthe partition may have a through hole located at the specific height,and the separate tank may have a structure in which the plating solutionin the first space passes through the through hole to flow into thesecond space.

Preferably, the electrolytic plating equipment according to the aboveembodiment further includes a source pipe that sends plating solutionfrom the plating tank to the separate tank, this source pipe has asupply port for supplying the plating solution to the first space, andthis supply port is located below the aforementioned specific height.

In this configuration, because the supply port of the source pipe islocated below the aforementioned specific height or in other words belowthe surface of the plating solution held in the first space, platingsolution supplied to the first space from the supply port can besupplied directly inside the plating solution held in the first space.When plating solution is thus directly supplied inside the platingsolution in the first space, the shock to the plating solution in thefirst space is less than when plating solution discharged once into airfrom the supply port falls the surface of plating solution held in thefirst space. Thus, the fluid movement of plating solution held in thefirst space can be controlled, and metal particles can be made to settlemore efficiently in the first space.

In the electrolytic plating equipment according to the above embodiment,when plating solution is discharged from the supply port towards theinner side of the separate tank, moreover, fluid movement of platingsolution held in the first space, and particularly movement of platingsolution in the lower part of the space, can be controlled better thanwhen the discharge is directed downward for example. In this way, it ispossible to control interference with settling of metal particles in thefirst space by preventing metal particles that have settled in the firstspace from being stirred up again.

The electrolytic plating equipment according to the above embodiment mayfurther includes a source pipe for sending the plating solution from theplating tank to the separate tank, the separate tank may have a firstpartition extending vertically so as to divide the separate tank intothe first space and the second space and a second partition extendingvertically so as to divide the first space into a settling space forsettling metal particles in the plating solution and a supply spacelocated upstream from the settling space wherein plating solution issupplied from the supply port of the source pipe.

In this configuration, because the first space is divided by the secondpartition into a settling space and a supply space, and the platingsolution is supplied to the supply space from the supply port of thesource pipe, the fluid movement of plating solution held in the supplyspace that occurs when plating solution is supplied to the supply spaceis unlikely to be communicated to the settling space. As a result, metalparticles can be made to settle more efficiently than if there were nosecond partition in the first space.

In the electrolytic plating equipment according to the above embodiment,when the second partition has a plurality of communicating holesprovided below the aforementioned specific height and communicatingbetween the settling space and the supply space, the plating solutionsupplied to the supply space is dispersed as it moves through themultiple communicating holes in the second partition into the settlingspace. Fluid movement of the plating solution held in the settling spacecan be controlled if the plating solution is dispersed in this way as itpasses through multiple communicating holes into the settling space.

In the electrolytic plating equipment according to the above embodiment,if the upper edge of the second partition is located at or below theaforementioned specific height, the height of the upper edge of thesecond partition will be the same as or lower than the surface of theplating solution held in the settling space. As a result, since thesurface of the plating solution in the settling space and the surface ofthe plating solution in the supply space are at roughly the same height,there is less shock when the plating solution flows from the supplyspace into the settling space. It is therefore possible to control thestirring up of metal particles that have settled in the settling spacefor example, and to prevent interference with settling of metalparticles in the settling space.

The electrolytic plating equipment according to the above embodiment mayfurther includes: a return pipe for returning plating solution from theseparate tank to the plating tank; and a re-supply pipe for returningplating solution discharged from the separate tank back to the firstspace. In this configuration, part of the plating solution in theseparate tank can be re-supplied to the first space via the re-supplypipe before being returned to the plating tank. This allows foreignmatter in the plating solution to be separated more efficiently.

In the electrolytic plating equipment according to the above embodiment,when a mechanical agitator further includes a mechanical agitatorprovided in a space downstream from the first space, the platingsolution can be agitated with this mechanical agitator in the downstreamspace after the metal particles have settled in the first space. Thisallows fine adjustments to be made to the dissolved oxygen concentrationof the plating solution.

In the electrolytic plating equipment according to the above embodiment,the plating tank may have: a tank body for holding plating solution; andan overflow tank provided integrally with the tank body in which theplating solution from the tank body overflows the upper edge of the sidewall of the tank body to flow into the overflow tank, and this overflowtank may contain an upstream space and a downstream space locateddownstream from the upstream space, and the plating solution fallsthrough air to flow from the upstream space into the downstream space.

In this configuration, the dissolved oxygen concentration of the platingsolution can be adjusted not only in the separate tank but also in theoverflow tank of the plating tank. In this overflow tank, the dissolvedoxygen concentration is adjusted as the plating solution falls throughair when flowing from the upstream space into the downstream space.

In the electrolytic plating equipment according to the above embodiment,when the upper edge of the tank body has a extending portion extendingtowards the overflow tank, and this extending portion has an end that isseparated from the side of the tank body, the plating solution flowingfrom the tank body into the overflow tank is conducted along theextending portion to the end of the extending portion, where itseparates from the extending portion and is released into air. As aresult, in this configuration the plating solution can be restrainedfrom flowing along the side wall of the tank body. This increases thecontact area of the plating solution with air when the plating solutionfalls, and allows the dissolved oxygen concentration of the platingsolution to be adjusted more efficiently.

In the electrolytic plating equipment according to the above embodiment,a drop through which the plating solution falls through air in thesecond space is preferably 10 cm or more. The dissolved oxygenconcentration of the plating solution in the separate tank can beadjusted still more efficiently if this drop is 10 cm or more.

The electrolytic plating method of this embodiment uses an electrolyticplating equipment provided with a plating tank for holding platingsolution, and a separate tank separated from this plating tank, with theplating solution circulating between the plating tank and the separatetank. The separate tank contains a first space and a second spacelocated downstream from the first space. In this method, the first spaceis filled with plating solution up to a specific height, and metalparticles in the plating solution are allowed to settle at the bottom ofthe first space. In this method, moreover, that part of the platingsolution in the first space that exceeds the specific height flows intothe second space, and the dissolved oxygen concentration of the platingsolution is adjusted by causing it to fall through air in this secondspace. In this way, the dissolved oxygen concentration of the platingsolution can be adjusted, while metal particles can be effectivelyremoved from the plating solution.

In the electrolytic plating equipment and electrolytic plating methodaccording to the above embodiment, the plating solution is used forcopper plating, which is particularly desirable when a sulfur-containingorganic compound is included as a brightener.

The present invention is explained in more detail below using examples,but the present invention is not limited by these examples.

Example 1

Objects to be plated (Samples Nos. 1 to 8) were copper electroplatedunder the following conditions using an electrolytic plating equipment.The electrolytic plating equipment 11 shown in FIG. 12 was used forSamples Nos. 2 to 4. In this electrolytic plating equipment 11, platingtank 13 has the same structure shown in FIG. 1, while separate tank 15has a structure in which separate tank body 20 is divided by firstpartition 21 and third partition 91 into three spaces: first space 17,second space 19 and third space 93. The plating solution overflows theupper edge of first partition 21 to flow from first space 17 into secondspace 19, and overflows the upper edge of third partition 91 to flowfrom second space 19 into third space 93. Second space 19 is equippedwith underflow divider 45.

For Samples Nos. 1 and 5 to 8, partitions 21 and 91 were removed fromseparate tank 15 of the electrolytic plating equipment 11 shown in FIG.12.

As shown in Table 2 below, the structures of the upper edges of firstpartition 21 and third partition 91 are Structure A (structure shown inFIG. 2D) in the case of Sample No. 4 and Structure B (structure shown inFIG. 2E) in the case of Samples Nos. 2 and 3.

The drop from the upper edges of first partition 21 and third partition91 to the surface of the plating solution was set to three levels, 5 cm,10 cm and 20 cm, as shown in Table 2 below.

Stainless steel plates and substrates with blind via holes (printedboards with blind via holes) were used as the objects to be plated(cathodes). The opening size of the blind via hole in the plate was 100μm, and the blind via hole depth was 75 μm.

The other electrolytic copper plating conditions were as follows.

Bath volume of plating tank 13 (combined bath volume of tank body 47 andoverflow tank 49): 4300 liters

Bath volume of separate tank 15 (combined bath volume of first space 17,second space 19 and third space 93): 800 liters

Bath volume: 5100 liters

Plating solution: Copper sulfate plating solution (containing 200 g/Lcopper sulfate pentahydrate, 50 g/L sulfuric acid and 50 mg/L chlorideions).

Additive added to plating solution: C.Uyemura “Thru-Cup EVF-T”

Plating solution circulation speed: 860 liters/minute

Anodes: Soluble anodes (titanium case filled with sulfur-containingcopper balls, enclosed in a polypropylene anode back)

The objects to be plated were copper electroplated under theseconditions, and the dissolved oxygen concentration, coating properties,and pit of the blind via hole were evaluated. The coating properties(elongation and tensile strength) were evaluated using theaforementioned stainless steel plates plated with 50 μm of copper.Pitting of the blind via holes was evaluated using the aforementionedsubstrates with blind via holes plated with 20 μm of copper.

In this Example 1, the stainless steel plates were pretreated, copperelectroplated, and post-treated in the following steps 1 to 8.

Step 1: Acid wash cleaner (C.Uyemura “MSC-3-A”)

Step 2: Hot water wash

Step 3: Water wash

Step 4: Acid wash

Step 5: Water wash

Step 6: Electrolytic copper plating

Step 7: Water wash

Step 8: Dry

The substrates with blind via holes were desmeared and chemically copperplated (0.3 μm) by well-known methods, and then pretreated, copperelectroplated, and post-treated by the same steps 1 to 8.

The electrolytic copper plating conditions in Example 1 were as shown inTable 1. The electrolytic copper plating temperature (plating solutiontemperature) was 25° C. The cathode current density is given in Table 1in units of A/dm².

TABLE 1 Stainless steel Substrate with plate blind via hole Cathodecurrent 1.0 1.0 density (ASD) Plating time 226 90 (minutes) Platingthickness 50 20 (μm)

The results are shown in Table 2. Table 3 gives the test procedures foreach sample. Table 4 shows the dissolved oxygen concentration after 30,60 and 90 minutes of electrolysis with the partitions 21 and 91 shown inFIG. 12 attached to the separate tank after plating of Sample No. 1 wascompleted. In order to maintain a roughly uniform flow volume of platingsolution to the object to be plated (cathode 57) from each nozzle 61,part of the plating solution supplied to tank body 47 via return pipe 41was supplied via pipe end 41 c. The dissolved oxygen concentration ofplating solution collected from a valve (not shown) attached to the pipenear pipe end 41 c in FIG. 12 was measured.

Pitting of the via was evaluated by first applying copper plating 103 asshown in FIG. 15B to the substrate with blind via hole 101 shown in FIG.15A, and then measuring the difference Δh in height (dimension indirection of thickness) between the lowest part of the surface of copperplating 103 formed inside blind via hole 101 c and the surface of copperplating 103 formed around blind via hole 101 c (FIG. 15B). Substratewith blind via hole 101 in FIG. 15A is provided with resin layer 101 aand copper layer 101 b formed on the surface of this resin layer 101 a,with blind via hole 101 c formed therein.

Elongation and tensile strength were measured as follows using the testpiece shown in FIG. 16. That is, a stainless steel plate was copperplated to 50 μ±5 μm, and the copper plating layer (copper foil) waspeeled carefully from the stainless steel plate so as to avoid wrinklesor damage. This copper foil was heat treated for 2 hours at 120° C., andthen punched with a dumbbell to the shape shown in FIG. 16 to prepare atest piece. The film thickness at the center of this test piece wasmeasured with a fluorescence x-ray film thickness meter, and themeasured value was taken as the film thickness d (mm) of the test piece.Next, the test piece was fixed between the chucks of a tensile testerwith a distance of 40 mm between chucks, and with the part of the testpiece having a round portion exposed outside the chucks, and tested at atension rate of 4 mm/minute. Next, the maximum tensile strength F (kgf)was derived from a chart obtained from the test, and this F (kgf) wasdivided by the cross-sectional area of the test piece to obtain thetensile strength values (kgf/mm²) shown in Tables 2, 6 and 9. Thecross-sectional area of the test piece was the width 10 mm of the centerof the test piece times the film thickness dmm. The elongation E (%) wascalculated by first measuring the elongation ΔL (mm) from the beginningof tension to breakage of the test piece, and then dividing this ΔL (mm)by the dimension (20 mm) of the straight part of the central part of thetest piece before tension.

TABLE 2 Dissolved Coating properties Separate oxygen Tensile BlindSample tank specs concentration Elongation strength via hole No.Partition Drop Circulation mg/liter (%) (kgf/mm²) pit μm 1 No partition— 10 turns 2.4 25.6 35.6 28.5 2 Structure B  5 cm 10 turns 3.7 31.2 32.419.2 3 Structure B 20 cm 10 turns 7.7 32 33.1 15.2 4 Structure A 10 cm10 turns 7.4 31.5 32.8 14.5 5 No partition 10 turns 6 32 33 15.2 6 Nopartition 10 turns 4.3 30.7 32.2 16.3 7 No partition 10 turns 3.4 31.133.3 18.1 8 No partition 10 turns 2.6 31 33.3 24.4

TABLE 3 Sample No. 1 Electrolyzed for 30 hours at cathode currentdensity 1.0 ASD using separate tank with no partition. Stainless steelplate and substrate with blind via hole then plated. 2 Electrolyzed for24 hours at 1.0 ASD using separate tank shown in FIG. 14. Stainlesssteel plate and substrate with blind via hole then plated. 3Electrolyzed for 24 hours at 1.0 ASD using separate tank shown in FIG.14. Stainless steel plate and substrate with blind via hole then plated.4 Electrolyzed for 24 hours at 1.0 ASD using separate tank shown in FIG.14. Stainless steel plate and substrate with blind via hole then plated.5 Electrolyzed for 8 hours following Sample No. 4 with plating solutioncirculating using separate tank with no partition. Stainless steel plateand substrate with blind via hole then plated. 6 Electrolyzed for 8hours following Sample No. 5 with plating solution circulating usingseparate tank with no partition. Stainless steel plate and substratewith blind via hole then plated. 7 Electrolyzed for 8 hours followingSample No. 6 with plating solution circulating using separate tank withno partition. Stainless steel plate and substrate with blind via holethen plated. 8 Electrolyzed for 8 hours following Sample No. 7 withplating solution circulating using separate tank with no partition.Stainless steel plate and substrate with blind via hole then plated.

TABLE 4 Dissolved oxygen Electrolysis time (minutes) concentration(mg/liter) 30 4 60 5.9 90 7.6

From the results for Sample No. 1 in Table 2, it can be seen that usinga separate tank without partitions 21 and 91, the dissolved oxygenconcentration of the plating solution was low, and the amount of pit inthe blind via holes tended to be greater.

From the results for Samples Nos. 2 to 4, it can be seen that thedissolved oxygen concentration is increased by providing partitions 21and 91 in separate tank 15 to cause overflow of the plating solution.The dissolved oxygen concentration is increased dramatically byproviding a drop of 10 cm or more for the plating solution duringoverflow as in Samples Nos. 3 and 4. In the case of these Samples Nos. 3and 4, the dissolved oxygen concentration did not decrease even afterlong-term electrolysis.

From the results for Samples Nos. 5 to 8, which were plated after SampleNo. 4, it can be seen that when partitions 21 and 91 are removed fromseparate tank 15, the dissolved oxygen concentration after duringlong-term electrolysis, and the amount of pit in the blind via holetends to increase.

As shown in Table 4, moreover, the dissolved oxygen concentrationincreased over time during electrolysis with partitions 21 and 91attached to the separate tank following plating of Sample No. 1.

Example 2

Objects to be plated (Samples Nos. 9 to 14) were copper electroplatedunder the following conditions using the electrolytic plating equipmentshown in FIG. 13A and FIG. 13B. A separate tank having the samepartitions 21 and 91 as the equipment of FIG. 12 was used as separatetank 15 for Samples Nos. 12 to 14. As shown in FIG. 13A and FIG. 13B,moreover, plating tank 13 was provided with tank body 47 and overflowtank 49, so that plating solution overflowing from tank body 47 flowedinto overflow tank 49. A plate-shaped object to be plated was arrangedroughly horizontally in tank body 47 as cathode 57, and multiple anodes55 were arranged above and below this cathode 57. Nozzles 61 were alsoarranged above and below cathode 57. Each nozzle 61 was provided withmultiple spray nozzles (not shown) for spraying plating solutionsupplied from separate tank 15 via return pipe 41 in the direction ofcathode 57.

For Samples Nos. 9 to 11, partitions 21 and 91 were removed fromseparate tank 15.

The drop of the plating solution from the upper edges of first partition21 and third partition 91 to the surface of the plating solution was setto three heights as shown in Table 6 below: 5 cm, 10 cm and 20 cm.

A stainless steel plate and a plate with through hole were used as theobjects to be plated (cathodes). The inner diameter of the through holein the plate was 0.3 mm, and the plate thickness was 1.6 mm.

The other electrolytic copper plating conditions and the like were asfollows.

Bath volume of plating tank 13 (combined bath volume of tank body 47 andoverflow tank 49): 1000 liters

Bath volume of separate tank 15 (combined bath volume of first space 17,second space 19 and third space 93): 1400 liters

Capacity: 2400 liters

Plating solution: Copper sulfate plating solution (containing 100 g/Lcopper sulfate pentahydrate, 200 g/L sulfuric acid and 50 mg/L chlorideions)

Additive added to plating solution: C.Uyemura “Thru-Cup ETN”

Circulation speed of plating solution: 3000 liters/minute

Anodes: Insoluble anodes (Ti—Pt coated with indium oxide)

In this Example 2, the stainless steel plates were pre-treated, copperelectroplated and post-treated in the same steps 1 to 8 as in Example 1.

The plates with through holes were first desmeared and chemically copperplated (0.3 μm) by well-known methods as in Example 1, and thenpre-treated, copper electroplated and post-treated in the same steps 1to 8 as in Example 1.

The electrolytic copper plating conditions for Example 2 are shown inTable 5. The electrolytic copper plating temperature (temperature ofplating solution) was 25° C. The cathode current density is given inTable 5 in units of A/dm².

TABLE 5 Stainless steel Substrate with plate through hole Cathodecurrent 5.0 5.0 density (ASD) Plating time 45 27 (minutes) Platingthickness 50 30 (μm)

The objects to be plated were copper electroplated under theseconditions, and the dissolved oxygen concentration, coating properties,and through hole throwing power (TH-TP) were evaluated. The results areshown in Table 6. Table 7 gives the test procedures for each sample. Thedissolved oxygen concentration was evaluated by measuring dissolvedoxygen in plating solution collected from a valve (not shown) attachedto return pipe 41 downstream from filter 65 in FIG. 13.

The throwing power is defined as the ratio of the thickness of thecopper plating on the plate surface near the through hole to thethickness of the copper plating half way through the through hole. Thatis, as shown in FIG. 17, after copper plating 107 is performed tosubstrate 105 in which through hole 105 a is formed under theseconditions, the throwing power (TH-TP) is obtained by entering thethicknesses e and f of the copper plating halfway through the throughhole and the thicknesses a through d of the copper plating on thesurface of the plate near the through hole into the following Formula(5):

TH-TP(%)=2(e+f)/(a+b+c+d)×100  (5)

TABLE 6 Dissolved Coating properties Separate oxygen Tensile Sample tankspecs concentration Elongation strength TH- No. Partition DropCirculation mg/liter (%) (kgf/mm²) TP % 9 No Partition — 75 turns 7.430.4 33.6 75.7 10 No Partition — 75 turns 23.4 23.5 37.8 70.7 11 NoPartition — 75 turns 38.5 15.4 43.4 65.6 12 Structure B  5 cm 75 turns21.5 24.5 37.5 72.5 13 Structure B 20 cm 75 turns 15.6 30.3 31.2 76.2 14Structure A 10 cm 75 turns 18.5 30.1 32.2 75.6

TABLE 7 Sample No. 9 Stainless steel plate and substrate plated withplating solution circulated using separate tank without partition. 10Electrolyzed for 3 hours following Sample No. 9. Stainless steel plateand substrate then plated. 11 Electrolyzed for 3 hours following SampleNo. 10. Stainless steel plate and substrate then plated. 12 Electrolyzedfor 24 hours at cathode current density 5.0 ASD using separate tank withpartition. Stainless steel plate and substrate then plated. 13Electrolyzed for 24 hours at 5.0 ASD using separate tank with partition.Stainless steel plate and substrate then plated. 14 Electrolyzed for 24hours at 5.0 ASD using separate tank with partition. Stainless steelplate and substrate then plated.

The results for Sample No. 9 in Table 6 show good coating propertieswith a dissolved oxygen concentration of 7.4 mg/liter at the start ofplating. However, the results for Samples Nos. 10 and 11 show thedissolved oxygen concentration increasing as the electrolysis timeincreases, with poor coating properties and lower TH-TP for Sample No.10 after 3 hours, and poor coating properties and the TH-TP decreasingto 65.6% for Sample No. 11 after 6 hours.

In the case of Samples Nos. 12 to 14, on the other hand, the increase indissolved oxygen concentration was controlled by providing partitions 21and 91 in separate tank 15, causing overflow of the plating solution.The effect of controlling the increase in dissolved oxygen concentrationis particularly remarkable when the drop of the plating solution duringoverflow is 10 cm or more as in Samples Nos. 13 and 14. In the case ofthese Samples Nos. 13 and 14, it was possible to reduce the dissolvedoxygen concentration to 20 mg/liter or less, resulting in good coatingproperties with a TH-TP of 75% or more.

Example 3

Objects to be plated (Samples Nos. 15 to 18) were electrolytic copperplating under the following conditions using the electrolytic platingequipment shown in FIG. 14. A separate tank having the same partitions21 and 91 as the equipment of FIG. 12 was used as separate tank 15 forplating Samples Nos. 17 and 18. Plating tank 13 is provided with tankbody 47 and overflow tank 49 as shown in FIG. 14, so that overflowingplating solution from tank body 47 flows into overflow tank 49.

The inside of tank body 47 is divided into two spaces by separatingmembrane 99. A Yuasa Membrane Systems “Y-9205T” was used for thisseparating membrane 99. An object to be plated was arranged as cathode57 in one space, while anode 55 was arranged in the other space. Nozzle61 was arranged near cathode 57. Nozzle 61 is provided with a spraynozzle (not shown) for spraying plating solution supplied from separatetank 15 via return pipe 41 in the direction of cathode 57.

For Samples Nos. 15 and 16, partitions 21 and 91 were removed fromseparate tank 15.

The drop of the plating solution from the upper edges of first partition21 and third partition 91 to the surface of the plating solution was setto two heights as shown in Table 9 below: 10 cm and 20 cm.

A stainless steel plate and a wafer with a blind via hole were used asthe objects to be plated (cathodes). The opening size of the blind viahole in the plate was 15 μm, and the blind via hole was 25 μm deep.

The other conditions for electrolytic copper plating were as follows.

Bath volume of plating tank 13 (combined bath volume of tank body 47 andoverflow tank 49): 50 liters

Bath volume of separate tank 15 (combined bath volume of first space 17,second space 19 and third space 93): 150 liters

Bath volume: 200 liters

Plating solution: Copper sulfate plating solution (containing 200 g/Lcopper sulfate pentahydrate, 50 g/L sulfuric acid and 50 mg/L chlorideions)

Additive added to plating solution: C.Uyemura “Thru-Cup ESA-21”

Circulation speed of plating solution: 100 liters/minute

Anodes: Soluble anodes (phosphor-containing copper balls enclosed in atitanium case)

In this Example 3, the stainless steel plates were pre-treated, copperelectroplated and post-treated in the same steps 1 to 8 as in Example 1.

The wafers were first given a barrier layer and seed layer by knownmethods, and then pre-treated, copper electroplated and post-treated inthe same steps 1 to 8 as in Example 1.

The conditions for electrolytic copper plating in Example 3 were asshown in Table 8. The electrolytic copper plating temperature(temperature of the plating solution) was 25° C. In Table 8, the cathodecurrent density is given in units of A/dm².

TABLE 8 Stainless steel plate Wafer Cathode current 1.0 1.0 density(ASD) Plating time 226 23 (minutes) Plating thickness 50 5 (μm)

The objects to be plated were copper electroplated under theseconditions, and the dissolved oxygen concentration, coating properties,and blind via hole pit were evaluated. The results are shown in Table 9.Table 10 gives the test procedures for each sample. The dissolved oxygenconcentration (DOC) was evaluated by measuring dissolved oxygen inplating solution collected from a valve (not shown) attached to returnpipe 41 downstream from filter 65 in FIG. 14.

During plating of Sample No. 15, air was agitated in first space 17 ofseparate tank 15 by using air agitator 94 to supply air to the platingsolution.

TABLE 9 Separate tank Coating properties specs Tensile Blind Air DOCElongation strength via hole No. Partition Drop cm agitation mg/liter %kgf/mm² pit μm Filter 15 No Partition — Use 3.8 30.5 33.4 7.4 Black 16No Partition — Not use 7.1 31.3 33.1 3.5 Replaced 17 Structure B 20 Notuse 7.7 30.7 32.6 2.7 White 18 Structure A 10 Not use 7.5 31.4 32.3 3.3White

TABLE 10 Sample No. 15 Electrolyzed for 24 hours at cathode currentdensity 1.0 ASD using separate tank without partition. 16 Stainlesssteel plate and substrate plated immediately after replacement of filterfollowing plating of Sample No. 15. 17 Electrolyzed for 24 hours at 1.0ASD using separate tank with partition. Stainless steel plate andsubstrate then plated. 18 Electrolyzed for 24 hours at 1.0 ASD usingseparate tank with partition. Stainless steel plate and substrate thenplated.

In the case of Sample No. 15 in Table 9, which was electrolyzed with airagitation in first space 17 of separate tank 15, the dissolved oxygenconcentration of plating tank 13 was 3.8 mg/liter as shown in Table 9,while at the same time the dissolved oxygen concentration of separatetank 15 was 7.2 mg/liter. Thus, the dissolved oxygen concentration ofthe separate tank can be maintained within a good range by means of airagitation, but because air agitation interfered with settling of copperparticles in first space 17, many copper particles were found adheringto filter 65 (filter 65 was black as shown in Table 9). Since dissolvedoxygen is expended by these copper particles adhering to filter 65, thedissolved oxygen concentration in the plating tank declines, and pit ofthe blind via hole tends to increase.

The results for Sample No. 16 show almost no copper particles adheringto filter 65 immediately after replacement, with a good dissolved oxygenconcentration in the plating tank and little pit of the blind via hole.

In the case of Samples Nos. 17 and 18, there were almost no copperparticles adhering to filter 65 (which was a white as new), indicatingeffective settling of copper particles in first space 17. Causingplating to overflow a partition provided in the separate tank in thisway is an effective way not only of increasing the dissolved oxygenconcentration but also of separating out copper particles from theplating solution. The dissolved oxygen concentration in the plating tankis also maintained within a desirable range, and pit of the blind viahole is reduced.

Reference Examples

The dissolved oxygen concentration, brightener concentration and Arvalue of the plating solution were measured by cyclic voltammetricstripping (CVS).

The method for measuring CVS is as follows.

1) Ar Measurement Method

A rotating platinum electrode as the working electrode, a copper bar asthe counter electrode and a silver/silver chloride double junctionelectrode as the reference electrode were immersed in the platingsolution, the potential supplied to the rotating platinum electrode wasvaried as the plating step, stripping step and washing step wererepeated, a potential-current curve (voltammogram) was prepared, and thearea in the stripping step (Ar value) was derived from thispotential-current curve.

The results shown in Tables 11 and 12 below were obtained by applyingthe CVS measurement method described above, and show changes over timein Ar values obtained by continuous repeated scanning in this method.

2) Measurement Instrument and Measurement Conditions Used in ArMeasurement

Measurement Instrument: ECI “QL-5”

Measurement conditions: Rotating platinum electrode rpm:

2500; potential sweep speed: 100 mV/second; temperature: 25° C.

3) Measurement Solution

The measurement solution was prepared as follows. 30 mL of the VMSdescribed below was placed in a container, and 30 mL of the platingsolution to be measured was added and mixed to obtain the measurementliquid.

4) VMS and Plating Solutions to be Measured

The plating solutions to be measured are shown in Table 11 for SamplesNos. 19 to 23 and in Table 12 for Samples Nos. 24 to 28. That is, in thecase of Sample No. 19 the plating solution to be measured is platingsolution collected from a valve (not shown) attached to a pipe near pipeend 41 c in FIG. 12 during plating of Sample No. 1 in Example 1, whilein the case of Sample No. 20, the plating solution to be measured isplating solution collected at the same location during plating of SampleNo. 3 in Example 1. In the case of Sample No. 24, the plating solutionto be measured is plating solution collected from a valve (not shown)attached to return pipe 41 downstream from filter 65 in FIG. 13 duringplating of Sample No. 11 in Example 2, while in the case of Sample No.25 the plating solution to be measured is plating solution collected atthe same location during plating of Sample No. 13 in Example 2.

In the case of Samples Nos. 21 to 23 and Samples Nos. 26 to 28, theplating solution to be measured was prepared in a beaker so as to obtainthe values shown in Tables 11 and 12 for dissolved oxygen concentration(DOC) of each measurement liquid after preparation for each sample.

C.Uyemura “Thru-Cup EVF-T” was used as the additive in the platingsolutions to be measured for Samples Nos. 19 to 23, while C.Uyemura“Thru-Cup ETN” was used as the additive in the plating solutions to bemeasured for Samples Nos. 24 to 28.

For Samples Nos. 19 to 23 in Table 11, a copper sulfate plating solution(containing 200 g/L copper sulfate pentahydrate, 50 g/L sulfuric acidand 50 mg/L chloride ions) was used as the virgin makeup solution (VMS),while for Samples Nos. 24 to 28 in Table 12, a copper sulfate platingsolution (containing 100 g/L copper sulfate pentahydrate, 200 g/Lsulfuric acid and 50 mg/L chloride ions) was used.

5) Measurement Results

The measurement results are shown in Table 11 and Table 12.

TABLE 11 Plating Ar value (mC) Sample solution DOC Brightener 15 30 4560 75 90 105 120 No. measured Additive (mg/L) (%) 0 min min min min minmin min min 19 Sample 1 EVF-T 2.4 100 1.249 1.2 1.176 1.166 1.163 1.161.157 1.152 1.155 Solution 20 Sample 3 7.7 100 1.142 1.143 1.144 1.1451.144 1.144 1.144 1.142 1.142 Solution 21 Beaker 8 100 1.155 1.158 1.161.162 1.157 1.158 1.157 1.16 1.157 makeup bath 22 Beaker 8 200 1.2111.212 1.214 1.209 1.207 1.21 1.214 1.218 1.213 makeup bath 23 Beaker 820 1.11 1.104 1.111 1.113 1.114 1.111 1.104 1.1 1.102 makeup bath

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TABLE 12 Plating Ar value (mC) Sample solution DOC Brightener 15 30 4560 75 90 105 120 No. measured Additive (mg/L) (%) 0 min min min min minmin min min 24 Sample 11 ETN 38.5 100 1.907 1.918 1.923 1.935 1.95 1.9551.959 1.963 1.964 solution 25 Sample 13 15.6 100 1.967 1.965 1.963 1.9631.963 1.965 1.966 1.964 1.967 solution 26 Beaker 8 100 1.97 1.973 1.9731.974 1.972 1.969 1.972 1.973 1.975 makeup bath 27 Beaker 8 200 2.012.009 2.012 2.013 2.011 2.008 2.007 2.008 2.009 makeup bath 28 Beaker 820 1.899 1.89 1.892 1.892 1.892 1.9 1.9 1.898 1.893 makeup bath

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The measured Ar value reflects the concentration of the brightener. InTable 11, the Ar value is about 1.14 to 1.16 when the dissolved oxygenconcentration and brightener concentration are suitable as in SamplesNos. 20 and 21. When the brightener concentration is suitable but thedissolved oxygen concentration is too low as in Sample No. 19, theinitial Ar value is about 1.2, which is about what it is when thebrightener concentration is too high (Sample No. 22). Over time, the Arvalue for this Sample No. 19 drops to about 1.15, or about the same asfor Sample No. 20.

In Table 12, the Ar value is about 1.97 when the dissolved oxygenconcentration and brightener concentration suitable as in Samples Nos.25 and 26. When the brightener concentration is suitable but thedissolved oxygen concentration is excessive as in Sample No. 24, theinitial Ar is about 1.91, which is about what it is when the brightenerconcentration is too low (Sample No. 28). Over time, the Ar value forthis Sample No. 24 rises to about 1.96, or about the same as for SampleNo. 25.

The reason why the Ar values for Samples Nos. 19 and 24 above approachthe Ar values for Samples No. 20 and 25 over time is as follows. Thatis, when potential scanning is repeated continuously, air dissolves intothe measurement liquid, and the dissolved oxygen concentrationfluctuates as shown in Tables 11 and 12, approaching the suitableconcentration. Air dissolves into the measurement liquid because it isbeing agitated by the rotating platinum electrode, and because thedissolved oxygen concentration of the VMS is close to the saturationconcentration of air.

This application is based on Japanese Patent Application No. 2009-207286filed on Sep. 8, 2009, the contents of which are hereby incorporated byreference.

What is claimed is:
 1. An electrolytic plating equipment comprising: aplating tank for holding plating solution; and a separate tank apartfrom the plating tank, for holding the plating solution circulatingbetween the plating tank and the separate tank, wherein the separatetank has therein a first space and a second space located downstreamfrom the first space, and has a structure in which the plating solutionin the first space in an amount exceeding a specific height flows fromthe first space into the second space, and the plating solution fallsthrough air in the second space.
 2. The electrolytic plating equipmentaccording to claim 1, wherein the separate tank has a partitionextending vertically so as to divide the separate tank into the firstspace and the second space, and has a structure in which the platingsolution in the first space overflows an upper edge located at thespecific height on the partition to flow into the second space.
 3. Theelectrolytic plating equipment according to claim 1, wherein theseparate tank has a partition extending vertically so as to divide theseparate tank into the first space and the second space, the partitionhas a through hole located at the specific height, and the separate tankhas a structure in which the plating solution in the first space passesthrough the through hole to flow into the second space.
 4. Theelectrolytic plating equipment according to claim 2, wherein the upperedge of the partition has a extending portion extending towards thesecond space, and the extending portion has an end separated from theside surface of the partition.
 5. The electrolytic plating equipmentaccording to claim 4, wherein the extending portion has a lateral partextending laterally towards the second space and a lower part extendingdownwards from a lateral end of the lateral part, and the end of theextending portion is a lower end of the lower part, the lower end isseparated from the side surface of the partition.
 6. The electrolyticplating equipment according to claim 1, further comprising a source pipefor sending the plating solution from the plating tank to the separatetank, wherein the source pipe has a supply port for supplying theplating solution to the first space, and the supply port is locatedbelow the specific height.
 7. The electrolytic plating equipmentaccording to claim 6, wherein the plating solution is discharged fromthe supply port towards the inner side of the separate tank.
 8. Theelectrolytic plating equipment according to claim 1, further comprisinga source pipe for sending the plating solution from the plating tank tothe separate tank, wherein the separate tank has a first partitionextending vertically so as to divide the separate tank into the firstspace and the second space and a second partition extending verticallyso as to divide the interior of the first space into a settling spacefor settling metal particles in the plating solution and a supply spacelocated upstream from the settling space for holding the platingsolution supplied from the supply port of the source pipe.
 9. Theelectrolytic plating equipment according to claim 8, wherein the secondpartition has a plurality of communicating holes provided below thespecific height for communicating between the settling space and thesupply space.
 10. The electrolytic plating equipment according to claim8, wherein the upper edge of the second partition is located at or belowthe specific height.
 11. The electrolytic plating equipment according toclaim 1, further comprising: a return pipe for returning the platingsolution from the separate tank to the plating tank; and a re-supplypipe for returning the plating solution discharged from the separatetank to the first space.
 12. The electrolytic plating equipmentaccording to claim 1, further comprising a mechanical agitator providedin a space downstream from the first space.
 13. The electrolytic platingequipment according to claim 1, wherein the plating tank has: a tankbody for holding the plating solution; and an overflow tank providedintegrally with the tank body in which the plating solution from thetank body overflows the upper edge of the side wall of the tank body toflow into the overflow tank, and the overflow tank has an upstream spaceand a downstream space located downstream from the upstream space, andthe plating solution falls through air to flow from the upstream spaceinto the downstream space.
 14. The electrolytic plating equipmentaccording to claim 13, wherein the upper edge of the tank body has aextending portion extending towards the overflow tank, and the extendingportion has an end that is separated from the side surface of the tankbody.
 15. The electrolytic plating equipment according to claim 1,wherein a drop through which the plating solution falls through air inthe second space is 10 cm or more.
 16. The electrolytic platingequipment according to claim 1, wherein the plating solution is used forcopper plating, and contains a sulfur-containing organic compound as abrightener.
 17. An electrolytic plating method using an electrolyticplating equipment including: a plating tank for holding platingsolution; and a separate tank apart from the plating tank, for holdingthe plating solution circulating between the plating tank and theseparate tank, wherein the separate tank has therein a first space and asecond space located downstream from the first space, and theelectrolytic plating method comprises: retaining the plating solution upto a specific height in the first space so that metal particles in theplating solution settle to the bottom of the first space; and making theplating solution in the first space in an amount exceeding the specificheight flow into the second space so that the plating solution is madeto fall through air in the second space to thereby adjust the dissolvedoxygen concentration of the plating solution.
 18. The electrolyticplating method according to claim 17, wherein the plating solution isused for copper plating, and contains a sulfur-containing organiccompound as a brightener.